1. Field of the Invention
The present invention relates to a printing press such as a multi-color press. In particular, the present invention relates to a construction of a blanket cylinder disposed in each printing unit of the printing press and, more particularly, to a cylindrical blanket that forms an outer peripheral surface of the blanket cylinder.
2. Description of Related Art
An offset rotary press (printing press) is provided with a plurality of printing units corresponding to colors to be printed. Each of the printing units is configured so as to distribute ink appropriately to form a thin ink film in a process in which ink charged in an ink fountain is transferred successively by an ink roller group arranged in a row. The formed ink film is transferred to a press plate wound around a plate cylinder, and after the ink film is transferred to the outer peripheral surface of a blanket cylinder, printing is performed on a web ruining while being brought into contact with the rotating blanket cylinders.
The outer peripheral surface of the blanket cylinder, which consists of an elastic member mainly made of rubber or the like, is liable to be subjected to permanent setting, breakage, and other damage, and therefore may need to be replaced. For this reason, the outer peripheral surface of the blanket cylinder has so far been constructed so as to be removable. FIGS. 3 to 5 are schematic views showing typical constructions of conventional blanket cylinders. These figures show a printing unit capable of doing perfecting (printing on both sides of a web) by disposing the blanket cylinders on both sides of a sheet pass line in an opposed manner.
FIGS. 3(a) and 3(b) show a construction of a blanket cylinder of a type such that a sheet-form blanket is wound around a basic shaft roller. As shown in these drawing figures., a blanket cylinder 30 is formed with a slit-form groove 16 over the whole length in the axial direction in the outer peripheral surface of a basic shaft roller 24. The blanket cylinder 30 is configured so that both ends in the circumferential direction of a sheet-form blanket 15 are inserted into the groove 16 so as to be held (fixed) by a tightening device 23. A member denoted by reference numeral 12 in FIG. 3(a) is a plate cylinder, and a member denoted by reference numeral 13 is a press plate. Both ends in the circumferential direction of the press plate 13 are gripped by a gripping portion 12a provided in the outer peripheral surface of the plate cylinder 12 so that the press plate 13 is wound on the outer peripheral surface of the plate cylinder 12. Also, a web 14 runs while being held between the upper and lower blanket cylinders 30, 30.
The blanket cylinder 30 of this type has a problem in that the work efficiency in replacing the blanket 15 is low, so that the replacement work takes much time. Also, the blanket 15 is subjected to a high tension in the vicinity of the tightening device 23 and is less prone to be subjected to a tension in a portion distant from the tightening device 23. Therefore, the blanket cylinder 30 also has a problem in that the thickness of the blanket 15 undesirably changes depending on the tension, so that the initial cylinder accuracy is poor and therefore the printing quality varies. Further, the blanket cylinder 30 also has problems in that rotating vibrations and noise are generated by the slit-form groove 16 opened in the axial direction in the cylinder surface of the tightening device 23, and in that much spoilage is produced because the slit-form groove 16 provides a non-printing portion.
FIGS. 4(a), 4(b) and 5 show a blanket cylinder of a type such that a cylindrical (sleeve-form) blanket is fitted on a basic shaft roller. As shown in FIGS. 4(a) and 4(b), a blanket cylinder 31 is configured so that a cylindrical blanket 10 is fitted onto the outer peripheral surface of a basic shaft roller 3. The cylindrical blanket 10 is constructed by integrally fitting a skin layer 17 formed of an elastic material, such as rubber, on a metallic sleeve 8. Also, as shown in FIG. 5, the cylindrical blanket 10 is rotatably supported between frames 5a, 5b by bearings 6a, 6b fitted in bushes 7a, 7b. Therefore, the work for attaching and detaching the cylindrical blanket 10 to and from the shaft roller 3 is performed in the state in which one bearing 6a together with the bush 7a is once removed from frame 5a to form a predetermined space, and thereby the shaft roller 3 is supported on one side by the other bearing 6b. 
In the end portion of the outer peripheral surface of the shaft roller 3 on the side on which the cylindrical blanket 10 is attached or detached, a plurality of air holes 18 are formed in the circumferential direction. These air holes 18 communicate with an air supply hole 19 formed in the shaft roller 3, and are connected to an air compression source 22 via a pipe 20, a solenoid valve 21, and the like, so that compressed air can be blown out in the radial direction through the air holes 18 at proper timing. The supply of compressed air toward the air holes 18 forms a compressed air layer in a gap between the shaft roller 3 and the cylindrical blanket 10. This compressed air layer increases the inside diameter of the cylindrical blanket 10 so that the cylindrical blanket 10 can be attached and detached easily to and from the shaft roller 3. The inside diameter of the cylindrical blanket 10 is formed so as to be slightly smaller than the outside diameter of the shaft roller 3. At the time of operation after fitting, therefore, the supply of compressed air is stopped, by which the cylindrical blanket 10 is contracted so as to come into close contact with the shaft roller 3.
For the blanket cylinder 31 of this type having the above-described configuration, the formation of the slit-form groove 16 in the outer peripheral surface of the shaft roller 3, which is necessary for the before-mentioned blanket cylinder 30, is unnecessary, and the time taken for the blanket to be replaced can be shortened. Also, since there is no joint on the surface of the blanket 10, a non-printing portion on the. blanket cylinder 31 is eliminated, and the non-printing portion is decreased to only the range of a portion where the press plate 13 is fitted to the plate cylinder 12, by which spoilage can be decreased. Also, since there is no joint on the surface and variations in thickness of blanket are small, the cylinder accuracy is increased so that vibration noise is reduced, and also the printing quality is stabilized from the early stage.
When the web 14 passes through the printing units successively, ink and moistening water are supplied to the web 14, so that the moisture content of the web 14 increases gradually, with the result that the web 14 becomes liable to elongate in the running direction. In the rotary press for doing multi-color printing by arranging a plurality of printing units, therefore, the elongation is accumulated increasingly toward the downstream side, so that the tension acting on the web 14 tends to decrease gradually.
To cope with this problem, a method can be conceived in which as shown in FIG. 6, for example, the diameters D1, D2 and D3 of blanket cylinders 31, 32, and 33 are relatively increased successively toward the downstream side in the running direction of the web 14 (D1 less than D2 less than D3) and the peripheral speeds V1, V2 and V3 of the blanket cylinders 31, 32 and 33 are slightly increased successively (V1 less than V2 less than V3), by which the elongation of the web 14 is absorbed to prevent the decrease in the tension. Also, a method can be conceived in which the rubber material on the outer peripheral surface of each blanket cylinder is made of a material having different paper feed characteristics, and the decrease in the tension is prevented by changing the paper feed characteristics without changing the diameters of the blanket cylinders.
In the aforementioned blanket cylinder 30 shown in FIGS. 3(a) AND 3(b), an undersheet is interposed between the shaft roller 3 and the sheet-form blanket 15, and by changing the thickness of the undersheet, the diameter of the blanket can be changed relatively easily. Further, even if a fluctuation in web tension level occurs between colors, the web tension is easily equalized because a tension drop occurs for each rotation in the portion of the slit-form groove 16 formed in the outer peripheral surface of the shaft roller 24.
In the blanket cylinder 31 shown in FIGS. 4(a) and 4(b), since there is no joint on the outer peripheral surface of the cylindrical blanket 10, the equalization of web tension caused by tension drop, as in the above-described blanket cylinder 30, cannot be expected. Also, since the cylindrical blanket 10 is manufactured by integrating the metallic sleeve 8 with the skin layer 17 formed of an elastic material, in order to change the diameter of the blanket cylinder 31, the thickness of the skin layer 17 must be changed. Alternatively, when the diameter of the blanket cylinder 31 is unchanged, the characteristics (paper feed characteristics) of the skin layer 17 must be changed.
Thereupon, in the rotary press equipped with the aforementioned blanket cylinder 31, cylindrical blankets 10 with different diameters or characteristics must be prepared for each color (for each printing unit), so that interchangeability of the cylindrical blankets 10 between the blanket cylinders 31 is lost. As a result, not only the stocks of spare parts increase and therefore the storage space increases, but also the manufacturing cost of individual cylindrical blanket 10 becomes high.
The present invention has been made to solve the above problems, and accordingly an object thereof is to provide a cylindrical blanket and a blanket cylinder, and a printing press, in which when multi-color printing is done on a running web by using a plurality of printing units arranged in a row, web tension in the running direction can be made uniform while vibrations and noise are restrained.
To achieve the above object, a cylindrical blanket in accordance with the present invention comprises a cylindrical sleeve; an elastic layer formed integrally with the sleeve by winding and bonding a sheet-form elastic member on and to the outer peripheral surface of the sleeve, the elastic layer having a gap extending in the axial direction formed between both ends in the circumferential direction of the sheet-form elastic member; and a separation preventive member for preventing both ends in the circumferential direction of the sheet-form elastic member from being separated from the sleeve, the separation preventive member being embedded in the gap so as to be thinner than the thickness of the sheet-form elastic member to form a groove in the outer peripheral surface of the elastic layer.
Preferably, the separation preventive member is an elastic member.
Also, a blanket cylinder in accordance with the present invention comprises a cylindrical blanket described above; and a shaft roller on which the cylindrical blanket is fitted, the cylindrical blanket being configured so as to be attached and detached freely to and from the shaft roller.
Also, a printing press in accordance with the present invention is configured so that a plurality of printing units are arranged in a row along a running line of a web to do printing on the web by using the printing units, the printing units each being fitted with a blanket cylinder described above. In particular, when perfecting is done, that is, when a pair of the blanket cylinders are arranged on the opposite sides of the running line of the web, the phase relation of the blanket cylinders is preferably established so that grooves formed in the outer peripheral surfaces of the paired blanket cylinders face each other on the running line of the web.
As described above in detail, according to the cylindrical blanket in accordance with the present invention, the groove extending in the axial direction is formed in the elastic layer formed on the outer peripheral surface of the cylindrical sleeve. Therefore, the cylindrical blanket has an effect that when the cylindrical blanket is disposed in each printing unit for a rotary press for multi-color printing, web tension in the running direction can be made uniform, and the cylinder accuracy can be increased by the integration of the elastic layer with the sleeve, so that the occurrence of vibrations and noise can be restrained.
In particular, since the elastic layer is formed by winding and bonding the sheet-form elastic member on and to the outer peripheral surface of sleeve, and the groove is formed by providing the gap between both ends in the circumferential direction of the sheet-form elastic member, the cylindrical blanket also has an effect that the manufacture can be made easily and the manufacturing cost can be saved. Also, in this case, the cylindrical blanket has an effect that both ends in the circumferential direction of the sheet-form elastic member can be prevented from being separated from the sleeve by embedding the separation preventive member the thickness of which is smaller than the thickness of the sheet-form elastic member in the gap, so that the frequency of replacement due to expired service life can be reduced.
Also, according to the blanket cylinder in accordance with the present invention, the above-described cylindrical blanket can be attached and detached freely to and from the shaft roller. Therefore, the blanket cylinder has an effect that the cylindrical blanket can be replaced easily, in addition to the effects achieved by the cylindrical blanket.
Also, according to the printing press in accordance with the present invention, the above-described blanket cylinder is disposed in each printing unit, by which web tension can be made uniform on the upstream and downstream sides of the blanket cylinder. Therefore, the printing press has an effect that the cylindrical blankets with different specifications such as diameter and paper feed characteristics need not be prepared, and only the cylindrical blankets with single specifications suffice. In particular, when perfecting is done, the printing press has an effect that a tension drop is made great and thereby the web tension can be made further uniform by establishing the phase relation of the blanket cylinders so that grooves formed in the outer peripheral surfaces of the paired blanket cylinders face each other on the running line of the web.